There is a large body of clinical and epidemiological evidence that hyperhomocysteinemia may be a critical pathogenic factor in the progression of end-stage renal disease (ESRD) and in the development of cardiovascular complications related to ESRD. Despite extensive clinical studies demonstrating the association of hyperhomocysteinemia with ESRD, it remains unknown whether elevations of plasma homocysteine (Hcys) levels can lead directly to the development of glomerular injury in ESRD. In this proposal, we hypothesize that elevations of plasma Hcys produce glomerular dysfunction and consequent sclerosis. We propose that this occurs independently of arterial blood pressure and contributes to the great susceptibility to glomerulosclerosis in the Dahl S rat model of hypertension. We will first determine whether chronic elevations of plasma Hcys levels result in glomerular dysfunction and injury in the rats with experimental hyperhomocysteinemia and explore the mechanisms mediating the sclerotic effects of Hcys in the glomeruli. Since nitric oxide (NO) and superoxide have been reported to importantly contribute to hyperhomocysteinemia-induced abnormality of extracellular matrix metabolism and arteriosclerosis, we will examine the effects of chronic hyperhomocysteinemia on NO and superoxide levels or related enzyme activity in the glomeruli by fluorescence microscopic imaging analysis and fluorescence spectrometry. Then, we will determine whether hyperhomocysteinemia contributes to glomerular injury in Dahl S rats and whether decreases in plasma Hcys levels associated with a choline and vitamin B therapy regimen prevent the rapid progression of glomerular damages in these rats. We will also explore the renal mechanisms increasing plasma Hcys levels by characterizing the biochemical pathways responsible for the abnormal metabolism of Hcys in the kidney of Dahl S rats using the kinetic analysis of enzyme activities with HPLC techniques and by expression analysis of related genes. The results of these studies will clarify the role of hyperhomocysteinemia as a risk factor or pathogenic factor in glomerular dysfunction and injury in ESRD and provide new insights into the mechanism contributing to the susceptibility and progression of glomerular injury associated with hypertension.